1. Field of the Invention
The present invention relates to a control apparatus for controlling an automotive generator installed on a vehicle according to a detected value of an electric current flowing through a field circuit of the generator and, more particularly, the invention pertains to an automotive generator control apparatus which is less susceptible to external noise or disturbances in detecting the value of an electric current flowing in a field circuit of the generator.
2. Description of the Background Art
Today, a common approach to improving fuel economy of an engine of a vehicle is to employ a system in which a control unit of the vehicle monitors power generation conditions of an automotive generator, estimates the amount of generator driving torque and controls engine speed, for instance. There exist some conventionally known methods of monitoring the amount of power generated by an automotive generator. One known method is to monitor the rate of switching on/off actions of a field current controlling transistor. This method however has a problem that the transistor ON/OFF rate does not necessarily correspond to the amount of the generator driving torque depending on operating conditions of the generator. Under such circumstances, there has been a need for a method of obtaining highly accurate information on the amount of power generated by the automotive generator. A solution to this problem is to monitor the value of a field current. For example, Japanese Patent Application Publication No. 2002-281792 discloses some methods of monitoring the value of a field current.
Since the value of a field current flowing in a field circuit of an automotive generator can be used as an important parameter for controlling the generator, it is necessary to monitor the field current value if the same is to be used for control purposes. Currently, there is a need for on-line transmission of the field current value to an engine control system. To alleviate work load applied to an electronic control unit (ECU) provided in a vehicle and to reduce the influence of noise induced in a transmission line, it is advantageous if the generator incorporates an analog-to-digital (A/D) converter so that the field current value is A/D-converted on the generator side and a resultant digital value is transmitted to the ECU.
A/D converters widely used in industrial applications are so-called successive approximation type A/D converters. Generally, the automotive generator is disposed in an engine room where the generator is exposed to extremely harsh ambient conditions so that the A/D converter, if used for controlling the generator, might be adversely affected by noise. The successive approximation type A/D converter determines the value of each bit by the method of false position, or the regula falsi method. Therefore, if noise is induced during execution of sampling operation by the A/D converter, a large amount of calculation error is likely to occur. Consequently, if the A/D converter of this kind is used in the automotive generator, there arises a problem that it is difficult to transmit a highly reliable field current value to the ECU.